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Self-employed & tax / Solo 401(k) Contribution Calculator

Solo 401(k) Contribution Calculator

US rates · checked 20 Oct 2026
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Schedule C line 31 (or your share of partnership SE income), after business expenses.

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2026 IRS limit. Check irs.gov for the year you're contributing for. The limit is per person across all your 401(k) and 403(b) plans.

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2026 IRS annual additions limit (section 415(c)). Check irs.gov for other years.

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2026 IRS cap on compensation a plan can count. Check irs.gov for other years.

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2026 SSA figure, used for the SE tax step. Check ssa.gov for other years.

Maximum solo 401(k) contribution
$43,087.05
$24,500.00employee deferral
$18,587.05employer contribution
43.1%share of net profit
$0net profit $100,000.00
  • SE tax
  • Employee deferral
  • Employer contribution
  • Rest of profit
Net profit$100,000.00
Self-employment tax · 15.3% on 92.35% of profit$14,129.55
Net SE earnings · profit − ½ SE tax$92,935.23
Employee deferral$24,500.00
Employer contribution · 20% of net SE earnings$18,587.05
Total contribution$43,087.05

Elective deferrals you made to an employer's 401(k) this year use up the same employee limit. Lower the deferral limit by that amount.

See breakdown

How the solo 401(k) contribution calculation works

Estimate the most you can put into a solo 401(k) as a self-employed owner: employee deferral, catch-up and employer contribution.

  1. Start from net self-employment earnings

    Take net profit and subtract half of your self-employment tax. $100,000 of profit has $14,129.55 of SE tax, leaving $92,935.23.

  2. Employer part: 20% of net SE earnings

    The plan's 25% rule works out to 20% for a sole proprietor, because the contribution itself reduces compensation. The IRS Publication 560 rate table converts a 25% plan rate to 0.200000. 20% of $92,935.23 is $18,587.05.

  3. Employee part: up to the deferral limit

    You can defer up to the yearly limit ($24,500 in 2026) as long as you have the earnings to cover it. At 50 or older a catch-up amount comes on top.

  4. Check the total cap

    Deferral plus employer contribution can't pass the annual additions limit ($72,000 in 2026). Catch-up contributions don't count toward it. Compensation above $360,000 (2026) is ignored.

Worked example. On $100,000 of net profit, SE tax is $14,129.55 and net SE earnings are $92,935.23. You can defer $24,500 as the employee and add $18,587.05 as the employer, a total of $43,087.05, about 43.1% of profit.

Solo 401(k) Contribution FAQ

How much can I contribute to a solo 401(k)?

The employee deferral limit plus 20% of net self-employment earnings, up to the annual additions limit. On $100,000 of profit that is about $43,087 with 2026 limits.

How is the solo 401(k) employer contribution calculated?

For a sole proprietor it is 20% of net profit minus half of SE tax. If you are paid W-2 wages from your own S corp, it is 25% of those wages instead, which this calculator doesn't cover.

What are the solo 401(k) contribution limits for 2026?

For 2026 the IRS limits are a $24,500 employee deferral, an $8,000 catch-up at 50 or older ($11,250 if you turn 60 to 63 in 2026), $72,000 in total before catch-up, and a $360,000 compensation limit. For 2025 they were $23,500, $7,500 and $70,000. The IRS announced the 2026 figures in news release IR-2025-111.

What is the solo 401(k) catch-up for ages 60 to 63?

SECURE 2.0 allows a higher catch-up of $11,250 in 2026 if you turn 60, 61, 62 or 63 during the year, instead of $8,000. On $100,000 of profit that raises the 2026 maximum from $43,087.05 to $54,337.05. Turn on the 50+ switch and enter $11,250 as the catch-up limit.

How much profit do I need to max out a solo 401(k)?

With 2026 limits, about $252,318 of net profit. At that level net SE earnings are about $237,500, so the $24,500 deferral plus the 20% employer part ($47,500) reach the $72,000 limit. Catch-up comes on top if you are 50 or older.

Does a 401(k) at my day job affect my solo 401(k)?

Yes, for the employee part. The deferral limit is per person, so deferrals at your job reduce what you can defer here. The employer contribution is separate.

Solo 401(k) vs SEP IRA: which allows more?

At the same profit, a solo 401(k) usually allows more because you add an employee deferral on top of the same 20% employer amount. On $100,000 of profit a SEP IRA allows $18,587.05 and a solo 401(k) $43,087.05 with 2026 limits. A SEP is simpler to run, and both share the $72,000 limit.

Is this tax advice?

No. It's an estimate using the IRS method for a sole proprietor. Plan documents, partnership income and other plans can change your limit, so confirm with your plan provider or tax preparer.

Sources: IRS: One-participant 401(k) plans · IRS Publication 560: Retirement plans for small business · IRS: COLA increases for dollar limitations (2026 limits) · IRS news release IR-2025-111: 401(k) limit increases to $24,500 for 2026

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